So-called lead-acid batteries are batteries in which the electrical current producing mechanism consists of a chemical reaction between certain lead compounds and an aqueous solution of sulfuric acid. Such batteries have been produced for well over one hundred years and have been used in a plurality of applications ranging from motive power propulsion to hand held audiovisual products. From humble beginnings, the lead-acid manufacturing industry has created a multibillion dollar world wide infrastructure truly indispensable to modern civilization.
Despite the enormous growth in volume, however, many of the manufacturing processes have changed very little, and in some cases not at all, since the first batteries were made a century ago. These early batteries consisted of two or more plates separated by a wooden separator and immersed in a solution of sulfuric acid in water. Each plate comprises a semi-rigid lead metal or lead-alloy grille-like structure whose openings are filled with a pasty mass of compounds which are mainly lead oxide, lead sulfates and water. Wooden separators are used to prevent the positive and negative plate from shorting out and rendering it useless. However these separators limited the life of the battery because they had an inherent stability problem in the battery acid solution and deteriorated in the high acid environment. A vast improvement was made when new, rubber-based separators were introduced. These separators ware stable in the battery acid and would allow the battery to no longer be limited by the life of the wooden separator. Unfortunately, the batteries could not be recharged fully and lost cap city. To fix this problem, ground up wood chips were added to the battery paste. The battery then could be recharged fully. It was subsequently determined that lignin was the chemical in the wooden separator which was essential to recharging the battery. Without it, the battery would not maintain its electrical capacity. This ingredient was identified as lignosulfonate, a material found in wood. This material influenced the battery's charge acceptance and its capacity. It is essential to the lead acid battery performance and is used in all lead acid batteries. Unfortunately, it was found that the lignosulfonate inhibited the formation of the battery plate. To overcome this slow process, carbon black was added to the paste. Carbon is considered an oxidation source in the battery, after the plates are formed, carbon black is likely a detractor from the life of the battery. Battery expanders contain carbon black, blanc fixe (barium sulfate) and lignosulfonate. The blanc fixe acts as a seed crystal for the lead to lead sulfate reaction. The blanc fixe must be fully dispersed in the paste in order for it to be effective. The lignosulfonate prevents the negative plate from forming a solid mass of lead sulfate during the discharge cycle. It enables the formation of long needle like crystals. The long crystals have more surface area and are easily converted back to the original state on charging. The carbon black increases the formation speed during the "curing" of the battery. Lignosulfonates inhibit the formation of the battery plate. The carbon black counteracts this problem.
Unfortunately, batteries are very sensitive to the type of lignin that is used. Lignin is a by-product of paper making and is sensitive to the type of tree harvested in addition to the papermaking process. Much testing must be done before each particular batch of lignin is determined to be suitable for use in a battery. The only reliable test method is to manufacture test batteries and check their charge acceptance over time. Once the particular batch of lignin is approved, it can be sold to other battery manufacturers to use in their batteries.
Another drawback of lignins is their heat sensitivity. They will breakdown in high temperature environments. The automotive battery industry is requiring smaller batteries which are just as efficient as the larger ones. The automobile is also placing the battery in areas that can be exposed.